A standalone water heater that "explodes" usually breaks at the bottom, creating a missile fully capable of going through a couple of floors and a roof.
The Mythbusters did a piece on it. The invention of the pressure relief valve probably saved thousands of lives of homeowners alone, not to mention some subset of pedestrians once the water heaters came back down.
Yes, I’ve seen both of their shows on water heater explosions.
The steam will quickly burn any exposed skin.